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H G Suárez

Publications and source records attributed to H G Suárez.

At least 19 recordsLinked to original sources
PubMed2002

Association of RET codon 691 polymorphism in radiation-induced human thyroid tumours with C-cell hyperplasia in peritumoural tissue.

The RET proto-oncogene encodes a protein structurally related to transmembrane receptors with an intracellular tyrosine kinase domain. In human thyroid gland, the RET proto-oncogene is normally expressed in parafollicular C-cells. Thyroid C-cell hyperplasia is associated with inherited medullary thyroid carcinomas and is considered as a pre-neoplastic stage of C-cells disease. It has also been observed in thyroid tissues adjacent to follicular and papillary carcinomas. In order to study the relationship between a misfunctioning of the RET proto-oncogene and the presence of C-cell hyperplasia, we compared a series of thyroid glands presenting sporadic or radiation-associated tumours, as well as samples of unrelated normal thyroid tissues, for alteration in exons 10 and 11 of the gene and for the presence or absence of C-cell hyperplasia. Here we report a significantly higher frequency of C-cell hyperplasia present in peritumoural thyroid tissues of radiation-induced epithelial thyroid tumours, than in peritumoural of sporadic thyroid tumours or in control normal thyroid tissues (P=0.001). A G691S RET polymorphism was present with a higher frequency in radiation-induced epithelial thyroid tumours (55%) than in sporadic tumours (20%) and in control normal thyroid tissues (15%). Interestingly, this polymorphism was associated in the majority (88%) of radiation-induced tumours with a C-cell hyperplasia in the peritumoural tissues. Several explanations for this association are discussed.

Adenoma↗
PubMed2000

Role of the cAMP and MAPK pathways in the transformation of mouse 3T3 fibroblasts by a TSHR gene constitutively activated by point mutation.

Constitutive activating mutations of the TSHR gene, have been detected in about 30 per cent of hyperfunctioning human thyroid adenomas and in a minority of differentiated thyroid carcinomas. The mutations activating the TSHR gene(s) in the thyroid carcinomas, were located at the codon 623 changing an Ala to a Ser (GCC-->TCC) or in codon 632 changing a Thr to Ala or Ile (ACC-->GCC or ACC-->ATC). In order to study if the constitutively activated TSHR gene(s) has played a role in the determination of the malignant phenotype presented by these tumors, we investigated: (1) the transforming capacity after transfection of mouse 3T3 cells, of a TSHR cDNA activated by an Ala-->Ser mutation in codon 623 or an Thr-->Ile mutation in codon 632 and (2) the pathway(s) eventually responsible(s) for the malignant phenotype of the cells transformed by these constitutively activated TSHR cDNAs. Our results show that (1) the TSHR(M623) or (M632) cDNAs give rise to 3T3 clones presenting a fully neoplastic phenotype (growth in agar and nude mouse tumorigenesis); this phenotype was weaker in the cells transformed by the 632 cDNA; (2) suggest that the fully transformed phenotype of our 3T3 cells, may be the consequence of the additive effect of the activation of at least two different pathways: the cAMP pathway through G(alpha)s and the Ras dependent MAPK pathway through G(beta)gamma and PI3K and (3) show that the PI3K isoform playing a key role as an effector in the MAPK pathway activation in our 3T3-transformed cells is PI3Kgamma. Signaling from PI3Kgamma to MAPK appears to require in our murine cellular system a tyrosine kinase (still not characterized), Shc, Grb2, Sos, Ras and Raf. It is proposed that the constitutively activated TSHR genes detected in the thyroid carcinomas, may have played an oncogenic role, participating in their development through these two pathways.

3T3 Cells↗
PubMed2000

Search for NTRK1 proto-oncogene rearrangements in human thyroid tumours originated after therapeutic radiation.

Rearrangements of NTRK1 proto-oncogene were detected in 'spontaneous' papillary thyroid carcinomas with a frequency varying from 5 to 25% in different studies. These rearrangements result in the formation of chimaeric genes composed of the tyrosine kinase domain of NTRK1 fused to 5' sequences of different genes. To investigate if the NTRK1 gene plays a role in radiation-induced thyroid carcinogenesis, we looked for the presence of NTRK1-activating rearrangements in 32 human thyroid tumours (16 follicular adenomas, 14 papillary carcinomas and two lymph-node metastases of papillary thyroid carcinomas) from patients who had received external radiation, using the reverse transcription polymerase chain reaction, Southern blot and direct sequencing techniques. These data were compared with those obtained in a series of 28 'spontaneous' benign and malignant thyroid tumours, collected from patients without a history of radiation exposure and four in vitro culture cell lines derived from 'spontaneous' thyroid cancers. Our results concerning the radiation-associated tumours showed that only rearrangements between NTRK1 and TPM3 genes (TRK oncogene) were detected in 2/14 papillary carcinomas and in one lymph-node metastasis of one of these papillary thyroid carcinomas. All the radiation-associated adenomas were negative. In the 'spontaneous' tumours, only one of the 14 papillary carcinomas and one of the four in vitro culture cell lines, derived from a papillary carcinoma, presented a NTRK1 rearrangement also with the TPM3 gene. Twenty-five of this series of radiation-associated tumours were previously studied for the ras and RET/PTC oncogenes. In conclusion, our data: (a) show that the overall frequency of NTRK1 rearrangements is similar between radiation-associated (2/31: 6%) and 'spontaneous' epithelial thyroid tumours (2/32: 6%). The frequency, if we consider exclusively the papillary carcinomas, is in both cases 12%; (b) show that the TRK oncogene plays a role in the development of a minority of radiation-associated papillary thyroid carcinomas but not in adenomas; and (c) confirm that RET/PTC rearrangements are the major genetic alteration associated with ionizing radiation-induced thyroid tumorigenesis.

Adenoma↗
PubMed2000

[Radiation-induced thyroid cancers].

Human epithelial thyroid radiation-induced tumorigenesis is the most frequent radiation-induced tumorigenic process in man. Results of different studies, concerning the molecular mecanism(s) of epithelial thyroid radiation-associated tumorigenesis show : 1) that there is not a significant difference in the frequency of activation of ras, gsp and trk proto-oncogenes between radiation-associated and < > thyroid tumors; 2) the relevant role played by RET/PTC ret proto-oncogene activating rearrangements, in the development of radiation-associated thyroid tumors originated after therapeutic radiation (mainly PTC 1) or the atomic accident of Chernobyl (mainly PTC 3) and 3) suggest that the patients who develop thyroid tumors after a history of irradiation, show a genomic instability consisting in a DNA repair defect.

Drosophila Proteins↗
PubMed1997

Oncogenic rearrangements of the ret proto-oncogene in thyroid tumors induced after exposure to ionizing radiation.

A high frequency (approximately 60%) of ret rearrangements in Chernobyl papillary thyroid carcinomas (PTC) has been reported recently. The data suggested that the radiation exposure may be a direct inducer of activating rearrangements in the ret gene. In our study, we have analyzed for the presence of RET/PTC oncogenes using the RT-PCR, XL-PCR, Southern blot and direct sequencing techniques, 39 human thyroid tumors from patients who had received external radiation for benign or malignant conditions. As controls, we studied 39 'spontaneous' tumors. Our results indicate that: 1) the overall frequency of ret rearrangements was 84% in papillary carcinomas (16/19) and 45% (9/20) in follicular adenomas; 2) in contrast with the results obtained in the Chernobyl tumors, the most frequently observed chimeric gene was RET/PTC1; and 3) all the tumors were negative for RET/PTC2. In the 'spontaneous' tumors, only the papillary carcinomas presented a ret rearrangement (15%: 3/20). Our data confirm the crucial role played by the ret proto-oncogene activating rearrangements in the development of radiation-associated thyroid tumors, and show, for the first time, the presence of RET/PTC genes in follicular adenomas appeared after external irradiation.

Adenoma↗
PubMed1997

High prevalence of activating ret proto-oncogene rearrangements, in thyroid tumors from patients who had received external radiation.

A high frequency (about 60%) of ret rearrangements in papillary thyroid carcinomas of children exposed to radioactive fallout in Belarus after the Chernobyl accident, has been reported by three recent studies (Fugazzola et al., 1995; Ito et al., 1994; Klugbauer et al., 1995). These studies suggested that the radiation exposure may be a direct inducer of activating rearrangements in the ret gene. In order to confirm the postulated link between irradiation and the role of the ret proto-oncogene in thyroid tumorigenesis, we analysed for the presence of ret activating rearrangements using RT-PCR, XL-PCR, Southern blot and direct sequencing techniques, 39 human thyroid tumors (19 papillary carcinomas and 20 follicular adenomas), from patients who had received external radiation for benign or malignant conditions. As controls, we studied 39 'spontaneous' tumors (20 papillary carcinomas and 19 follicular adenomas). Our data concerning the radiation-associated tumors, showed that: (1) the overall frequency of ret rearrangements was 84% in papillary carcinomas (16/19) and 45% (9/20) in follicular adenomas; (2) in contrast with the results obtained in the Chernobyl tumors, the most frequently observed chimeric gene was RET/PTC1 instead of the RET/PTC3 and (3) all the tumors were negative for RET/PTC2. In the 'spontaneous' tumors, only the papillary carcinomas presented a ret rearrangement (15%:3/20): 1 RET/PTC1, 1 RET/ PTC3 and 1 uncharacterized. In conclusion, our results confirm the crucial role played by the ret proto-oncogene activating rearrangements in the development of radiation-associated thyroid tumors appearing after therapeutic or accidental ionizing irradiation, and show, for the first time, the presence of RET/PTC genes in follicular adenomas appeared after external irradiation.

Adenoma↗
PubMed1995

Activating mutations of the TSH receptor in differentiated thyroid carcinomas.

A series of 14 thyroid carcinomas, characterized for their basal adenyl cyclase activity (ACA), was examined for the presence of activating point mutations in the TSH receptor (TSHR) gene. Sequencing of the carboxyl-part of this gene revealed the presence of a somatic and heterozygotic point mutation in codon 623 in three out of six tumors showing a constitutively enhanced ACA and a poor response to TSH stimulation. The mutation determines the substitution of a serine for an alanine in the third intracellular loop of the receptor, in a region critical for signal transduction. One tumor bearing a TSHR mutation presented also a N-ras point mutation. Both mutations were detected also in a lung metastasis of this tumor. Our data represent the first report of alterations in the TSHR gene in thyroid malign neoplasia. TSHR mutations may indeed participate, as well as the G alpha s protein (gsp oncogene), in the oncogenesis of some differentiated thyroid carcinomas presenting increased basal levels of cAMP and a poor response to TSH.

Adenocarcinoma, Follicular↗
PubMed1995

Pattern of ras and gsp oncogene mutations in radiation-associated human thyroid tumors.

The preferential activation of the Ki-ras oncogene in follicular radiation-associated human thyroid carcinomas, has been suggested by Wright et al. (1991). However, only 12 thyroid tumors were analysed in this study. In order to confirm if radiation favours, in human thyroid tumorigenesis, the appearance of a particular molecular lesion, we studied 33 benign and malignant human radiation-associated thyroid tumors. We used polymerase chain reaction (PCR) amplification and allele-specific hybridization with mutant-specific probes for the three ras genes and the gsp oncogene. Compared to 85 'spontaneous' human thyroid tumors, the radiation-associated cases: (1) show a similar overall frequency of ras and gsp mutations (about 30% and 6% respectively); (2) present a similar frequency of mutation of the three ras genes without any predominance in adenomas and papillary carcinomas and (3) all Ki-ras mutations were found in papillary carcinomas (4/15). ras and gsp genes were never found mutated simultaneously, suggesting an alternative role for both oncogenes in the thyroid tumorigenic radiation-associated process.

Adenoma↗
PubMed1993

Characterization of a c-met proto-oncogene activated in human xeroderma pigmentosum cells after treatment with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).

Human xeroderma pigmentosum (XP) fibroblasts were transformed with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The transformed cells, called ASKMN, were immortalized, grew in agar and were tumorigenic in nude mice. A trp-met oncogene was identified in ASKMN cells, after transfection of high molecular weight DNA on 3T3 mouse cells. The ASKMN cells and the 3T3 transformants expressed the 5-kb mRNA transcribed by the tpr-met oncogene and its p65tpr-met phosphorylated protein. Using the polymerase chain reaction (PCR) technique followed by hybridization with synthetic probes or direct sequencing, we showed that the sequence encompassing the 'rearranged breakpoint' was the same as that previously described in the tpr-met oncogene present in the MNNG-HOS cells. However, G to A transitions found in the tpr or met sequences of the ASKMN oncogene, probably the result of the specific mutagenic activity of MNNG, were absent in the MNNG-HOS gene. Apparently normal chromosomes 1 and 7 were identified in the ASKMN cell metaphases using several cytogenetic techniques.

Animals↗
PubMed1991

v-myb transformation of Xeroderma pigmentosum human fibroblasts: overexpression of the c-Ha-ras oncogene in the transformed cells.

Human Xeroderma pigmentosum "normal" fibroblasts AS16 (XP4 VI) were transformed after transfection with a recombinant v-myb clone. In this clone (pKXA 3457) derived from avian myeloblastosis virus (AMV), the expression of the oncogene sequences is driven by the AMV U-5 LTR promoter. The transformed cells (ASKXA), which have integrated a rearranged v-myb oncogene, grow in agar, are not tumorigenic in nude mice, and express a 45-kDa v-myb protein. The HMW DNA of these cells transform chicken embryo fibroblasts. The c-Ha-ras oncogene is overexpressed in the ASKXA cells but not in the parental "normal" AS16 cells and a revertant clone (ASKXA Cl 1.1 G). Our results lead to the conclusion that the XP fibroblasts are phenotypically transformed by the presence of the transfected v-myb oncogene, which is able to induce an overexpression of the c-Ha-ras gene.

Animals↗
PubMed1988

Detection of activated ras oncogenes in human thyroid carcinomas.

Focus formation following DNA transfection of mouse 3T3-Vill cells was used to search for the presence of activated oncogenes in human thyroid tumors. Oncogenes belonging to the ras family were detected in four out of six thyroid carcinomas (Ki-ras in one anaplastic tumor and one follicular moderately differentiated tumor and Ha-ras and N-ras in two papillary tumors). Normal thyroid tissue samples obtained from two patients, one with an anaplastic tumor and one with a benign adenoma, and samples from 4 benign adenomas and from one toxic goiter of a patient with Graves' disease gave negative results. In one case, restriction enzyme analysis demonstrated the presence of a mutation in codon 12 of the activated Ha-ras oncogene. Our data show that all three ras proto-oncogenes can become activated in malignant thyroid tumors.

Adenoma↗
PubMed1985

DNA-mediated transfer of actinomycin D resistance into cultured mouse cells.

The transfer of high molecular weight (HMW) DNA isolated from Syrian hamster actinomycin D-resistant cells (C12TSV5/R) to sensitive A9 mouse cells, resulted in the growth in selective medium of transferent clones A9 ActR C11, C12 and C13). The resistant mouse cells have presumably acquired a gene(s) conferring actinomycin D resistance and express a 140-150 K surface glycoprotein, apparently involved in the drug resistance.

Animals↗
PubMed1981

Enhancement of transcription of the SV40 genome in mouse embryo cells by pretreatment with 5-iodo-2'-deoxyuridine.

Treatment of mouse embryo (ME) cells with 5-iodo-2'-deoxyuridine (IdUrd) before infection with SV40 virus, enhances T-antigen (T-Ag) production as detected by immunofluorescence and complement fixation. Cellular DNA and RNA synthesis are inhibited in both SV40 and mock-infected cells after IdUrd treatment. The analogue pretreatment significantly increases the amount of radiolabelled nuclear and cytoplasmic SV40-specific RNA and the RNA polymerase activity of the viral transcriptional complexes of the Sarkosyl supernatants, suggesting that the enhancement of SV40 T-Ag production in infected pretreated ME cells results from an increased synthesis of early virus RNA.

Animals↗
PubMed1980

Simian virus 40-Chinese hamster kidney cell interaction. V. Cooperative effect of 5-iodo-2'-deoxyuridine and mitomycin C in the enhancement of virus replication in infected cells.

A cooperative effect of 5-iodo-2'-deoxyuridine and mitomycin C which amplified (10- to 50-fold) their stimulating effect on simian virus 40 replication was obtained in infected Chinese hamster kidney cells. The results indicate that these drugs act at different levels to modify the permissiveness of cells to simian virus 40.

Animals↗